Energy Partitioning, Dynamic Fragmentation, and Off‐Fault Damage in the Earthquake Source Volume
Energy Partitioning, Dynamic Fragmentation, and Off‐Fault Damage in the Earthquake Source Volume
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DOI：
10.1029/2021jb022616
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发表时间：
2021-11
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影响因子：
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通讯作者：
S. E. Johnson;W. Song;S. Vel;B. Song;C. Gerbi
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文献类型：
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作者：
S. E. Johnson;W. Song;S. Vel;B. Song;C. Gerbi
地震破裂或破裂能量表示在前进的破裂前缘和滑动的断层面周围的体积中消耗的能量。通常通过反演地面运动并使用结果来模拟断层表面上的滑动来获得估计。然而，这种做法无法确定不同能源消耗过程的贡献，因此我们对这些过程重要性的理解主要来自实地和实验室研究。在这里，我们使用石榴石碎片尺寸数据来估计表面积能量密度与距离的断层核心在一个深折返走滑断层/剪切带的损伤区。在动态破坏区的外部和内部，每次碎裂事件的估计能量密度分别为2.87 × 103至2.72 × 105 J/m3，动态区是根据碎片大小分布的分维和其他指标推断的。在动态损伤区的105 m宽度上进行积分，得到每单位断层面积的断裂表面积能量，范围从每事件6.63 × 105 J/m2的下限到1.63 × 107 J/m2的上限。这一范围与大多数地质学、理论和运动学滑动模型对地震矩>1017 N·m的震源体能量消耗的估计重叠。我们采用基于物理的破碎模型来估计与石榴石破碎相关的等效拉伸应变率，其范围为5.42 × 102至1.04 × 104 s-1/地震，分别在动态损伤区的外部和内部。我们的研究结果表明，地表能量的产生是地震能量收支的一个不可忽视的组成部分。
Seismological fracture or breakdown energy represents energy expended in a volume surrounding the advancing rupture front and the slipping fault surface. Estimates are commonly obtained by inverting ground motions and using the results to model slip on the fault surface. However, this practice cannot identify contributions from different energy‐consumption processes, so our understanding of the importance of these processes comes largely from field‐ and laboratory‐based studies. Here, we use garnet fragment size data to estimate surface‐area energy density with distance from the fault core in the damage zone of a deeply exhumed strike‐slip fault/shear zone. Estimated energy densities per fragmentation event range from 2.87 × 103 to 2.72 × 105 J/m3 in the outer and inner portions of the dynamic damage zone, respectively, with the dynamic zone being inferred from the fractal dimensions of fragment size distributions and other indicators. Integrating over the ∼105 m width of the dynamic damage zone gives fracture surface‐area energy per unit fault area ranging from a lower bound of 6.63 × 105 J/m2 to an upper bound of 1.63 × 107 J/m2 per event. This range overlaps with most geological, theoretical, and kinematic slip‐model estimates of energy expenditure in the source volume for earthquakes characterized by seismic moments >1017 N·m. We employ physics‐based fragmentation models to estimate equivalent tensile strain rates associated with garnet fragmentation, which range from 5.42 × 102 to 1.04 × 104 s−1 per earthquake in the outer and inner portions of the dynamic damage zone, respectively. Our results suggest that surface‐energy generation is a nonnegligible component of the earthquake energy budget.